Let is used to create a new local variable and set its value. A local variable is a variable that only exists within the brackets [] or procedure it was created in, unlike a global variable. It can only be used in the code that comes after its declaration, and takes the form of let variable-name initial-value.

For example,

let my-blue-friends turtles with [ color = blue and shape = “person” ] 
ask my-blue-friends [ forward 1 ]

creates a new variable called my-blue-friends and sets its value to all the blue person-shaped turtles. Then, asking my-blue-friends to move forward moves all blue person-shaped turtles forward. To change the value of the variable after creating it, use set.